This invention relates generally to controlled power transferring devices and deals more particularly with apparatus for controlling the transfer of power in an electrical induction device from a power source to a load without distorting or degrading the transferred power waveshape. More specifically, the present invention deals with power transferring devices of the type having a core selectively loaded by a variable reactance to control the power transfer.
It is often desirable to control or regulate the supply of alternating current electric power to a load under varying source power and varying load conditions. In some cases, such as, for example, where a load device is powered by a commercial, 60 Hertz power source, proper device operation is dependent upon the presence of a sinusoidal voltage having a nominal magnitude of typically 110 volts. When the magnitude of the voltage rises above or falls below the nominal value, inefficient or improper load operation may occur. In other instances, such as, for example, those occuring during a brownout when the source power drops well below the desired nominal value, actual damage may occur to the load device being powered. Consequently, a need exists for a power transferring device which provides a sinusoidal output voltage to power a load and additionally maintains output voltage regulation over a wide range of source power variations.
In certain other cases, it is desirable to control or regulate the supply of alternating current electric power to a load in response to a command signal from a device sensing for example, such parameters as voltage, current, temperature, humidity, motor speed or other such similar parameters. In these cases, a control circuit of some type generally cooperates with a feedback signal generated by the sensing device to regulate the power transfer.
Unlike many previously used regulating devices employing transformers, magnetic circuits and the like, the regulating characteristics of the present invention are not dependent upon operation along a specific portion of the power transferring device's B-H curve. Consequently, a particular shaped B-H curve and selection of the proper amount and type of core material is not critical in the present invention to provide regulation.
Still other applications, such as those relating to high voltage power transmission and distribution require that the output alternating current electric power waveshape remain sinusoidal and the magnitude of the output power provided to a user, such as a household or factory, remain constant over a wide range of load variations. When a heavy demand for power is made on power companies, more current flows in the power distribution lines. The increased current causes a higher voltage drop in the distribution lines, and consequently lowers the magnitude of the voltage provided to a user. The power companies generally compensate for the lower voltage at the user end of the distribution line by increasing the magnitude of the voltage provided at the source end of the distribution line. The increased voltage is often obtained by mechanically moving taps on a power distribution transformer or the like to control the power transfer to the distribution line to maintain the magnitude of the voltage provided to a user within predetermined limits. The power transferring device of the present invention does not require moving parts to control power transfer to increase or decrease the output voltage.
One previously used power transferring arrangement controls the rate of electric power transfer in an electrical induction device such as a transformer, by loading a core with a variable reactance produced by selectively short circuiting and open-circuiting a control coil at a predetermined time. This arrangement has the advantage of controlling large amounts of power with relatively low power handling control and circuit components. Generally, arrangements of this type achieve power transfer control by varying the time and accordingly the amount of power that is transferred to a load. The power transfer time control is often accomplished by using a phase shift control circuit to activate a short-circuiting switch means, such as an SCR or the like, at a predetermined phase angle during each alternating current electric cycle. A feedback means or manual adjustment cooperates with the phase shift control circuitry to select the phase angle. Such an arrangement is illustrated and described in my U.S. Pat. No. 3,938,030 entitled "Controllable Power Transferring Device Utilizing a Short-Circuited Controlled Reactance", issued Feb. 10, 1976.
Although the arrangement described in the above referenced patent is able to provide efficient power transfer and control, it has the disadvantage that the input power waveform is not preserved during the power transfer, and consequently, the transferred power waveform is distorted.
A general aim of the present invention is to provide apparatus for controlling the transfer of power from a power source to a load that overcomes the limitations of previously used power transferring devices.
Another aim of the present invention is to provide a power transferring device that does not distort or degrade the waveshape of the alternating current transferred power.
A further aim of the present invention is to provide a power transferring device that is self-regulating over a wide range of source power and load variations.
Other features and advantages of the present invention will be apparent from the following written description and the drawings forming a part thereof.